I created a mod called Pregunpowder Experiment to see if I could get more realistic behavior from TripleA. Due to the map admin problems, I can't approve yet, but you download it directly from https://github.com/triplea-maps/Pregunpowder_Experiment.
Here are the notes
*An experiment of strategic interactions in pre-gunpowder times. The only unit types are Infantry, Cavalry and Forts. Combat is limited to 3 rounds
Infantry is cheap to build and maintain but can't attack cavalry
Cavalry is expensive to build and maintain but has a higher combat factor and is faster. It can't attack forts.
Forts are expensive to build but cheap to maintain. They have 2 hits and AA type attack each round on all enemy units. There can be a maximum of 5 forts in a territory.* (Note that a long siege can destroy a large army).
The AI utilized units in an appropriate way but did not buy cavalry. The game has some of the feel of pregunpowder warfare with unopposed cavalry being devastating.
I will probably use some of these ideas in future mods.